Standard Operating Procedure for Usage and Regeneration of desiccants
1.0 Purpose:
The purpose of this document is to describe the procedure for usage and regeneration of desiccants.
2.0 Scope:
This procedure describes in details of usage and regeneration of different type of desiccant used in Quality Control at [Company Name].
3.0 Responsibility:
Quality Control Person: Responsible for Usage and regeneration of desiccants used in QC Laboratory
Manager / designee-Quality Control: Verify whether the SOP is followed.
QA designee: Check the compliance of activity.
4.0 Definition:
A desiccant is a hygroscopic substance that induces or sustains a state of dryness (desiccation) in its local vicinity in a moderately well-sealed container. Desiccant is a substance that absorbs moisture. It is most commonly used component to remove humidity which might degrade or even destroy products sensitive to moisture.
5.0 Procedure:
5.1. General information:
5.1.1. Generally silica gel, activated charcoal, calcium sulfate, calcium chloride, montmorillonite clay, and molecular sieves are used as desiccant.
5.1.2. Pre-packaged desiccant is most commonly used to remove excessive humidity.
5.1.3. A specific usage of a desiccant would be in insulated windows where it is placed inside the spacer between the air space and window edge. This prevents moisture condensation between the panes.
5.2. Usage of the Desiccants:
5.2.1. Drying and cleaning of air and gases. (Zero air, nitrogen, oxygen, hydrogen, acetylene etc.)
5.2.2. Optical instruments and devices. (FTIR , Spectrophotometer and auto-titrator)
5.2.3. Protection of transferring materials from moisture.
5.2.4. Drying and storage of standards.
5.2.5. Desiccators used in the laboratory (Colour indicating silica gel)
5.3. Regeneration of Desiccant:
5.3.1 Silica gel: Silica gel is a high porous form of silica which is made from sodium silicate. Although called a “gel”, it is actually in solid state. Follow the below instructions for regeneration of Silica gel.
5.3.1.1 Remove the silica gel kept in different desiccators and instruments.
5.3.1.2. Keep the collected silica gel in the drying oven into a flat tray.
5.3.1.3. Set the temperature of the oven to 110°C and allow the silica gel to reach equilibrium temperature.
5.3.1.4. Silica gel shall be allowed to remain in the oven at the assigned temperature for 8 hours.
5.3.1.5. At the end of the time period ensure that the silica gel shall be completely regenerated and then transfer in a desiccator jar or dry airtight container.
5.3.2 Silica Gel Packets: Silica Gel packets are usually used for preserving the quality of an object inside an enclosed package. Desiccant silica gel can absorb moisture making it very useful as a drying agent. After absorbing enough moisture, it may be regenerated by heating it in an oven. Follow the below instructions for regeneration of Desiccant silica gel packet.
5.3.2.1. Remove the silica gel packet kept in standard containers / Instruments and replace previously dried silica gel packet into the respective standard containers / Instruments.
5.3.2.2. Keep the collected silica gel packets in the oven into a flat tray.
5.3.2.3. Set the temperature of the oven to 105°C and allow the silica gel packets to reach equilibrium temperature.
5.3.2.4. Silica gel packets shall be allowed to remain in the oven at the assigned temperature for 8 hours.
5.3.2.5. At the end of the time period ensure that the silica gel shall be completely regenerated and then transfer in a desiccator jar or dry airtight container.
5.3.3 Molecular Sieves: A molecular sieve is a material containing tiny pores of a precise and uniform size that is used as an adsorbent for gasses and liquids. Molecular sieve absorbs up to 22% of its own weight and can hold moisture to temperatures well past 450°F (230°C), and because of its high affinity for moisture, molecular sieve is able to bring the relative humidity in packages down as low as 10% RH.
Follow the below instructions for regeneration of molecular sieve.
5.3.3.1. Remove the molecular sieve kept in different parts of Instruments / Equipment and replace with previously dried molecular sieve into the respective Instruments / Equipment
5.3.3.2. Keep the collected Molecular sieve in oven into a flat tray.
5.3.3.3. Set the temperature of the oven to 250°C and allow the molecular sieve to reach equilibrium temperature.
5.3.3.4. Molecular sieve shall be allowed to remain in the oven at the assigned temperature for 24 hours.
At the end of the time period ensure that the molecular sieve should be completely regenerated and then transfer in a desiccator jar or dry airtight container
5.4. Frequency of regeneration:
Regenerate all desiccants used in laboratory as and when required in following conditions.
5.4.1. When silica gel turns dark blue to light pink or white.
5.4.2. When molecular sieves turn light pink to dark brown or light gray
Note:
a. For Monthly frequency the allowable time is + 3 working days.
b. For half yearly frequency the allowable time is + 15 working days.
5.5. Storage of Activated Desiccants:
5.5.1 Regenerated desiccants should be stored in a tightly closed labeled container and keep the container in desiccators.
5.5.2 Keep the desiccators in cool and dry place.
5.5.3 Following table shows the Frequency of replacing the desiccants:
| Usage of Desiccants for | Desiccant used | Frequency of replacing the desiccants |
| Analytical Balance | Silica gel filled in Vial | Daily |
| UV- Visible Spectrometer | Silica gel (100gm pack) | Monthly |
| Potentiometer Titrator and KF | Molecular sieves | Monthly |
| FT-IR Spectrometer | Silica gel (100gm pack) | Monthly |
| FT-IR Spectrometer | window with molecular sieves | Six Monthly |
| Gas Chromatography | Silica gel | Six Monthly |
| Gas Chromatography | Molecular sieves | Six Monthly |
| Standard Storage | Silica gel (1gm pack) in each container | Monthly |
| Desiccators | Silica gel (Color indicating) | Monthly |
5.6. Expiry of the Desiccants:
5.6.1. Silica gel which remains white after regeneration shall not be used and it should be discarded properly.
5.6.2. Molecular sieves remain dark brown after regeneration shall not be used and it should be discarded properly.
6.0 Acceptance Criteria:
Not Applicable
7.0 Frequency:
As per table specified in the point no. 5.5.3
8.0 Format for recording:
8.1. Schedule for the replacement of the desiccants
| SR. NO. | Name of Instrument/ Equipment | Asset No. | Location | Desiccant replacement | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sept | Oct | Nov | Dec |
| Done on/ Sign |
Note:
a. For Monthly frequency (#) the allowable time is + 3 working days from the due date.
b. For half yearly frequency ($) the allowable time is + 15 working days from the due date.
8.2. Label for the desiccant replacement
